Thanks, those are good pointers... Do you also see a way to get a shiny new button saying "Send by Email" in the delivery order itself? We don't want to email all customers automatically.

Yes you can do that create email template from settings>>technical>> emails>> Template create template and click on button add to context. there is one button visible in more option of delivery. refer this link http://maheshwarimayur.blogspot.in/2012/12/send-mail-in-openerp-with-mail-templates.html